There has been known an LED element containing a GaN-based semiconductor layer formed on an SiC substrate (e.g. see Patent Literature 1). The LED element uses a fluorescent SiC substrate having a first SiC layer in which B and N are doped and a second SiC layer in which Al and N are doped and releases near-ultraviolet light from a multiple quantum well active layer. Near-ultraviolet light, which is absorbed in the first SiC layer and the second SiC layer, is converted from green visible light to red visible light in the first SiC layer and converted from blue visible light to red visible light in the second SiC layer. As a result, white light which is close to sunlight with a high rendering property is released from the fluorescent SiC substrate.
However, the LED element is accompanied by high dislocation density in the GaN-based semiconductor layer due to a lattice mismatch and a difference in the coefficient of thermal expansion between the SiC substrate and the GaN-based semiconductor layer. As a result, a problem arises with difficulty in increasing the thickness and lowering the resistance in the GaN-based semiconductor layer.
There is proposed a method to form a GaN film on a substrate via a buffer layer by MOCVD, after which nanocolumns are formed by etching the GaN film using metal and a dielectric nanomask in order to reduce dislocation density in a semiconductor layer on the substrate (e.g. see Patent Literature 2). According to this method, after formation of the nanocolumns, a GaN-based semiconductor layer is grown on the buffer layer and the nanocolumns by using lateral growth.